In various types of non-invasive imaging systems, radiation may be generated and transmitted through a volume of interest, in which may be placed a patient under examination, a piece of baggage or a parcel undergoing security screening, or an article of manufacture undergoing quality review. A portion of the radiation that passes through the volume impacts a digital detector or a photographic plate where the X-ray transmission data is collected. In digital X-ray systems a photodetector produces signals representative of the amount or intensity of radiation impacting discrete elements of a detector surface. The signals may then be processed to generate a two-dimensional or three-dimensional image that may be displayed for review.
In certain such non-invasive imaging systems, X-ray tubes or other X-ray generation technologies are used as the source of the radiation that is transmitted through the imaged volume. The X-rays are generally emitted in response to control signals that may be specified by a suitable examination protocol. Typically, the X-ray tube includes a cathode and an anode. An emitter within the cathode may emit a stream of electrons directed toward the anode. The anode may include a target that is impacted by the stream of electrons. The target may, as a result of impact by the electron beam, produce X-ray radiation that may be directed through an imaged volume of an imaging system.
In X-ray tubes, magnetic focusing may be used to focus the electron beam onto the target. However, it may be difficult to maintain the desired focal spot size for a respective imaging application on the target due to current changes that may occur with respect to the elements used to generate the magnetic fields used to focus the electron beam. That is, changes in the current passing through these magnetic field generating elements may result in undesired variance in the size of the focal spot where the electrons impact the target for a particular imaging application. Such variance in the size of the focal spot may lead to undesired image artifacts or reduced image quality.